Systemic administration of drugs treats the organism as a whole, even though the disease may be localized, such as occlusion of a duct or vessel. When administered to a patient systemically, many drugs, e.g., chemotherapeutic drugs such as those used to treat cancer and benign prostate hyperplasia, cause undesirable side effects. Localization of a drug poses special problems in cases involving the walls of ducts and vessels, since, by nature, these organs serve as transport systems.
Artherosclerotic disease, for example, causes localized occlusion of the blood vessels resulting from the build-up of plaque. As the deposits increase in size, they reduce the diameter of the arteries and impede blood circulation. Angioplasty, which involves the insertion of catheters, such as balloon catheters, through the occluded region of the blood vessel in order to expand it, has been used to treat artherosclerosis.
The aftermath of angioplasty in many cases is problematic, due to restenosis, or closing of the vessel, that can occur from causes including mechanical abrasion and the proliferation of smooth muscle cells stimulated by the angioplasty treatment. Restenosis may also occur as a result of clot formation following angioplasty, due to injury to the vessel wall which triggers the natural clot-forming reactions of the blood.